A leaching study was undertaken to examine the application of the atmospheric acid leaching process to a bulk copper concentrate for copper recovery followed by cyanidation or thiosulfate leaching for gold and silver recovery. A comprehensive analysis of leach solution and residues were undertaken and leaching rates compared at various conditions. For copper, the results indicated that lower pulp density and finer grinding enhances the leaching kinetics. Overall extraction for finer size concentrate at atmospheric leaching for 12 h was 88-89 % Cu. For essentially the same leaching conditions but a coarse grind the test yielded 83-84 % copper extraction. A single test was run at low oxygen over-pressure to ensure sufficient oxygen for ferrous-ferric catalysis to be fully effective. This test showed 91 % copper extraction for a finely ground concentrate which is a 2-3 % improvement over purely atmospheric leaching. Mineralogical studies conducted on samples from the leaching program indicated that the un-leached copper consisted predominantly of enargite (Cu3AsS4) and partially leached covellite (CuS). The enargite in particular showed a high level of liberation and was not reactive under the conditions of the leach testwork. Recovery of gold and silver from acid leach residues by cyanide leaching was partially successful. For the acid leach residues containing 1.0-1.7 % Cu, the gold extraction ranged between 41-44 % Au and the silver extraction was between 30-45 %. Calcium thiosulfate extracted 14.3 % gold in 24 h and 26.6 % gold in 48 h. With ammonium thiosulfate, the gold leaching was faster showing ~21.1 % gold extraction in 24 h but almost all leached gold precipitated in the following 24h because of excessive degradation of thiosulfate.
展开▼
